As linked over on the Chemistry Reddit, there’s sad news from a suburban Chicago High School to report. A 16 year old student at Richard High School in Oak Lawn was severely injured during a pressure demonstration when the apparatus his high school chemistry teacher was using to demonstrate increasing pressure failed.
Get this: the teacher allegedly put dry ice and some water in a plastic bottle, then tightly closed the lid. Then, allegedly he actually passed the bottle around the class so students could physically witness the buildup of pressure.
Dumb. Dumb. Dumb. Honestly, what was this chemistry teacher thinking? Apparently the students may not have even been given goggles to wear.
Who knows how many years the teacher has been doing this demo serendipitously without incident. Well, this time the bottle exploded while this student was holding the bottle. He can no longer see out of his left eye, and he suffered hearing damage and other injuries to his hands and face. It’s unclear from the reports if he physically lost the eye or lost his sight in that eye. The teacher is on administrative leave and the parents of the boy have filed suit. The parents are claiming “negligence, willful and wanton misconduct and vicarious liability” and are seeking more than $150,000 in damages.
Now, I’ve worked with pressurized dry ice before. For those of you who don’t know, dry ice is solid carbon dioxide. The solid carbon dioxide sublimes to gaseous carbon dioxide at room temperature and quickly becomes a gas with a volume much much larger than the original solid. If you put all this volume in a closed container, the pressure will build and build until the container fails and explodes. You make a bomb as soon as you put dry ice in a closed container. The addition of water accelerates the sublimation causing the pressure to build up faster.
I’ve done this demonstration before at ‘magic shows.’ We used a small amount of dry ice in a 2-L pop bottle. We were outside, we had the kids and team members a good 30-40 feet away behind a fence, and we covered the pop bottle with one of those plastic mail crates to absorb the force of the exploding bottle and contain any shrapnel.
It’s really loud. Even with the mail crate atop, the explosion still throws the bottle/crate 5-10 feet in the air. There’s absolutely nothing safe about this demonstration, and there’s no reason to have anyone anywhere near the bomb while the pressure is building. ESPECIALLY don’t have teenagers play hot potato with it! Geez!
I also blogged a while ago about using liquid carbon dioxide as a green extraction technique. To create the liquid carbon dioxide, you need to change the temperature and the pressure. Put some dry ice in a plastic centrifuge tube, cap the tube tight enough that the pressure builds, but loose enough that the gas can still escape through the threads, and submerge the centrifuge tube in warm water. The authors of the paper suggest the carbon dioxide inside the centrifuge tube approaches the triple point as it is converted into a liquid. The triple point of carbon dioxide is -56 degC, and 5.1 atm (the critical point is 31 degC and 72 atm). 5.1 atmospheres is still a big deal, and letting the gas buildup escape through the threads of the centrifuge cap is crucial to maintaining some semblance of control over the setup. I still got admonished in the comments to that post about the safety of the extraction and the setup I constructed.
Bottom line: there is no reason to callously put dry ice in a closed container. Just don’t do it. It really does make a bomb, and bombs really do destroy things. It’s just not worth it. In fact, making a dry ice bomb is illegal in most jurisdictions. As one Reddit commenter noted: “this is one of those experiments where a YouTube video will suffice.”